Based on the hypothesis that (a) DNA repair mechanisms, which can be modulated by genetic and environmental factors, influence mutation frequencies and (b) somatic mutagenesis, as well as derepression of certain regulatory genes, contribute to the carcinogenic process, the research proposal in this application will undertake the task of examining the genetic elements of mutagenesis and carcinogenesis in vitro. A new integrative theory of carcinogenesis, which states that carcinogens are agents which induce a stable transformation of a cell by either mutations and/or epigenetic alterations in the expression of certain regulatory genes of tissue specific transformation genes, will be the framework for in vitro somatic cell genetic analysis of human cells. With the use of human cells derived from patients genetically predisposed to cancer, with the use of BrdU-blacklight technique, and with the use of known tumor promoters, we will try to induce human transformation in vitro. Moreover, somatic cell hybrid technique will be used to isolate the chromosomes and genes responsible for DNA repair enzymes in human cells. Extension of initial studies on the potential DNA-repair deficient human syndrome (Cockayne) will be undertaken. Lastly, sensitive assays to distinguish carcinogenic mutagens from carcinogenic gene modulators will be developed. The use of sensitive assays to identify mutagenic carcinogens will also be included in our studies.